1. Field of the Invention
The present invention relates to a testing technique for a group of circuits. More particularly, the present invention relates to a testing technique for margin voltages of a plurality of circuits.
2. Description of Related Art
For most of integrated circuits (ICs), direct current (DC) voltage generators are generally applied therein. If the DC voltage generator provides an unsuitable voltage to the IC, it may lead to malfunction of the IC. Therefore, when fabrication of the IC is completed, the IC is generally tested to guarantee a production yield thereof. In the following content, a conventional circuit testing technique is described in detail with reference of a figure.
FIG. 1 is a schematic diagram illustrating a conventional method of adjusting voltages of a DC voltage generator via a fuse technique. Referring to FIG. 1, a circuit 11 includes a DC voltage generator 101 and a test mode trim unit 102. The DC voltage generator 101 is used for providing a DC voltage V1. The test mode trim unit 102 may trim the DC voltage V1 into a plurality of testing voltages Vout for testing whether or not the circuit 11 can work normally.
First, assuming an optimal working voltage of the circuit 11 is 2.5V, and a margin voltage thereof is 2.3V˜2.7V. Moreover, assuming the test mode trim unit 102 has 8 test modes shown as table 1.
TABLE 1the test modes of the test mode trim unit 102Shifting amount ofTest modethe DC voltage V1011−0.2 V010−0.1 V001−0.05 V 000    0 V100+0.05 V 101+0.1 V110+0.15 V 111+0.2 V
Generally, testing the circuit includes two stages, and in a first stage thereof, a testing voltage closest to the optimal working voltage is supplied to the circuit 11 for testing whether or not the circuit 11 can work normally. In a second stage, a margin voltage is supplied to the circuit 11 for testing whether or not the circuit 11 can work normally, so as to ensure a quality of the circuit 11.
Assuming the DC voltage V1 generated by the DC voltage generator 101 is 2.65V, in the first stage of circuit testing, to simulate whether or not the circuit 11 can work normally under the optimal working voltage, the test mode of the test mode trim unit 102 can be set to “0, 1, 0”, so as to shift the DC voltage V1 by −0.1V, and supply a 2.55V testing voltage to the circuit 11. Next, whether or not the circuit 11 can work normally under the margin voltage is tested. If the circuit 11 can work normally, it represents the circuit 11 can be repaired via the fuse technique, and if the circuit 11 cannot work normally, it represents the circuit 11 has a defect and cannot be shipped, so that purchase of malfunctioned circuits by customers can be avoided.
As described above, in the second stage of the circuit testing, to simulate whether or not the circuit 11 can work normally under the margin voltage, the test mode of the test mode trim unit 102 can be set to “1, 0, 0”, so as to shift the DC voltage V1 by +0.05V, and supply the 2.7V testing voltage Vout to the circuit 11. Therefore, whether or not the circuit 11 can work normally under the 2.7V margin voltage may be simulated by applying the 2.7V testing voltage Vout.
As described above, the test mode of the test mode trim unit 102 can be further changed to “0, 1, 1”, so as to shift the DC voltage V1 by −0.2V, and supply the 2.45V testing voltage to the circuit 11. Therefore, whether or not the circuit 11 can work normally under the 2.3V margin voltage may be simulated by applying the 2.45V testing voltage Vout. It should be noted that due to limitation of the test mode trim unit 102, it cannot provide the 2.3V testing voltage for simulating whether or not the circuit 11 can work normally under the 2.3V margin voltage. In other words, the aforementioned method cannot ensure that the circuit may work normally under the voltages 2.3V˜2.45V.
Besides, assuming there are one hundred circuits 11 required to be tested, since the DC voltages V1 generated by the DC voltage generators 101 of the circuits 11 are slightly different with each other, when the circuits are tested, the test mode trim units 102 of the one hundred circuits 11 have to be set one by one to generate suitable testing voltages. In detail, according to the conventional method, assuming testing time spent at the first stage and the second stage for testing each of the circuits 11 are respectively T1 and T2, a total time spent for testing the one hundred circuits 11 is then 100×(T1+T2). Therefore, the conventional method is very time-consuming and cost-consuming.
Referring to FIG. 1 again, assuming there are one hundred circuits 11 to be tested, to shorten the total time spent for testing the circuits 11, another method is provided according to the conventional method, and the method may be described as follows. In the first stage of the circuit testing, the 2.5V testing voltages V1 are simultaneously supplied to the one hundred circuits 11 by a testing machine (not shown), so as to test in parallel whether or not the one hundred circuits can work normally.
As described above, in the second stage of the circuit testing, first, the 2.3V testing voltages V1 are simultaneously supplied to the one hundred circuits 11 by the testing machine, so as to test in parallel whether or not the one hundred circuits can work normally. Next, the 2.7V testing voltages V1 are simultaneously supplied to the one hundred circuits 11 by the testing machine, so as to test in parallel whether or not the one hundred circuits can work normally. Though such method can reduce the total time spent for testing the circuits, it cannot ensure that the DC voltage generators 101 of the one hundred circuits 11 can work normally. In other words, if the DC voltage generator 101 of the circuit 11 has a defect, the circuit 11 then cannot work normally, and the conventional method cannot detect such defect of the DC voltage generator 101.
Moreover, since the testing voltage V1 provided by the testing machine is stable and has a powerful driving capability, if the circuit 11 has a defect such as current leakage, etc., shifting of the testing voltage V1 may still not occur. In other words, if the circuit 11 has the defect such as current leakage, etc., though the DC voltage generator 101 of the circuit 11 may provide the 2.5V working voltage to the circuit 11, the working voltage provided by the DC voltage generator 101 is shifted (for example, shifted to 2.0V) due to the current leakage of the circuit 11, so that the circuit 11 probably cannot work normally, and the conventional method cannot detect such defect, either.